The present invention generally relates to wound care requiring dressings and more specifically is directed towards a sterile cellular synthetic wound dressing made of polyvinyl acetal.
Throughout history, many diverse materials of various origins have been used to treat skin wounds. By 1923, the British Pharmaceutical Codex, included 97 surgical material products which included products generally listed as medicated and unmedicated cotton wools, gauzes, tows, and lints; gauze and cotton tissues, bandages, jaconet, oiled silk and emplastrums. Emplastrums consist of a piece of white leather, hand spread with a plaster mass having a generally medicated composition. By 1949, the number of these products had decreased; however, the practitioner of 1923 would probably have been surprised to find that products had hardly changed from the products used some twenty five years earlier. Until 1960, advances in the design of wound management products had been spasmodic and limited to the adaption of available materials. Little or no attention was paid to the performance of the product and little consideration was given to different healing environments which were required by different wound types. From 1960 on, a new generation of products was developed based on the realization that the control of micro-environments was necessary if wound healing was to progress to the optimum degree.
Advances in the development of synthetic polymers produced the most radical changes in the wound care dressings as factors such as water vapor, oxygen permeability, bacterial impermeability, and selective absorption could be incorporated into new formulations along with specific requirements such as conformability, non-adherence, and adhesiveness. This family of polymeric products included polymeric foams, polymeric films, particulate and fibrous polymers, hydrogels and hydrocolloids.
The polymeric foams along with polymeric films were the first to be described as environmental dressings. LYOFOAM.RTM. and CORADERM.RTM. are polyurethane foams with a heat and pressure modified wound contact surface having a limited absorbent capacity while permeable to water vapor with low adherence to the wound site. LYOFOAM.RTM. is a closed cell foam and has been used in the management of pressure ulcers while CORADERM.RTM. is a thinner polyurethane "membrane" and has been found useful in initiating healing in long-term ischemic ulcers.
Certain wounds require debridement to facilitate new cell growth and to that end particulate and fibrous polymeric products are used. Such materials debride wounds by entrapment of wound exudate which contains proteins, enzymes and growth factors. These enzymes will break down the necrotic tissue and loosen the bonds between the necrotic tissue and the wound's healing surface. Such materials preferably create a moist environment that will encourage autolytic debridement and may take the form of a granule, paste, fibrous mat, acrylamide/agarose copolymer sheet or twisted staple hank.
Hydrogels are three dimensional cross-linked networks of hydrophilic polymers that are prepared from materials such as gelatin, polysaccharides, cross-linked polyacrylamide polymers, polyelectrolyte complexes, and polymers or copolymers derived from methacrylate esters. These interact with aqueous solutions by swelling to an equilibrium value and retaining a significant proportion of water within their structure. They are insoluble in water. By varying the nature of the polymer structure a range of water-binding behavior and thus mechanical surface and permeability properties can be obtained. The absorption, transmission, and performance result in the maintenance of a moist wound with a continuous moisture flux across the dressing and a sorption gradient that assists in the removal of toxic components from the wound area.
In contrast to the single polymer hydrogels described, the products designated as hydrocolloids are complex formulations that contain not only colloids but elastomeric and adhesive components. Hydrocollids have an adhesive formulation that gives an initial adhesion higher than some surgical adhesive tapes. After application, the absorption of transepidermal water vapor will modify the adhesive flow to maintain a high tack and adhesive performance throughout the period of use.
The optimum wound handling characteristics for products are expressed in general terms such as a) removal of excess exudate and toxic components; b) maintain a high humidity or moistness at the wound/dressing interface; c) allow gaseous exchange; d) provide thermal insulation; e) protect against secondary infection; f) free wound from particulate contaminants; and g) allow removal of dressing from patient without pain or trauma. Even with the advances in technology, it should be noted that there is no simple dressing that can produce the optimum micro environment for all wounds or for all the healing stages of a single wound.
Nurses classify the wound stage based on the following criteria.
Stage I: Erythema not resolving within 30 minutes of pressure relief. Epidermis remains intact. Reversible with intervention. PA1 Stage II: Partial thickness loss of skin layers involving epidermis and possibly penetrating into but not through dermis. May present as blistering with erythema and/or induration; wound base moist and pink; painful, free of necrotic tissue. PA1 Stage III: Full-thickness tissue loss extending through dermis to involve subcutaneous tissue. Presents as shallow crater unless covered by eschar. May include necrotic tissue undermining sinus tract formation, exudate and/or infection. Wound base is usually not painful. PA1 Stage IV: Deep tissue destruction extending through subcutaneous tissue to fascia and may involve muscle layers, joint, and/or bone. Presents as a deep crater, unless covered by eshcar. May include necrotic tissue, undermining, sinus tract formation, exudate, and/or infection. Wound base is usually not painful. "Standards and Protocol for Pressure Ulcer Care", Norma J. Mash, p. 97, Chronic Wound Care, .COPYRGT.1990. PA1 Necrosis, slough and eschar PA1 Prolonged inflammation PA1 Hypoxemia PA1 Vascular insufficiency PA1 Protein malnutrition PA1 Infection PA1 Steriod medications PA1 Dehydrated wound bed PA1 Anemia PA1 "How do you score? : Test your skills in Pressure Ulcer Management", p. 197, Joan E. Halpin-Landry, Chronic Wound Care, .COPYRGT.1990. PA1 1). Moisture vapor permeable membrane PA1 2). Polymeric membranes PA1 3). Hydrogel dressings PA1 4). Hydrocolloid semi-occlusive and occlusive dressings. "Using Synthetic Autolytic Debriding Agents for the Treatment of Full-Thickness Ulcers", Nora King, p. 97, Chronic Wound Care, .COPYRGT.1990.
A clean moist wound surface enhances cellular migration. Maintenance of wound surface temperature facilitates cellular activity. Impediments to wound healing include necrotic tissue, infection and excess or pooled exudate. Necrotic tissue is an impediment to wound healing and can be removed through several techniques. There are a number of acceptable methods of debridement, including sharp debridement by cutting; mechanical debridement typically performed with a gauze, soft brush or sponge; gauze dressing debridement wet-to-dry and wet-to-wet; fluid bath or water propulsion; chemical or enzymatic debridement. Surgical debridement provides rapid and effective removal of necrotic tissue. Conventional debridement provides rapid and effective removal of necrotic tissue and can be used with other conventional topical surgery to enhance the clean-up of the wound. Enzymatic agents chemically break down necrotic tissue and transparent adhesive film dressings enhance leukocyte migration and resultant autolysis of necrotic tissue. Chronic Wound Care (supra.), pp. 101, 102.
Wound cleansing promotes removal of wound debris and bacteria from the wound surface; absorptive dressings are used to absorb excess exudate, obliterate dead space, and keep the wound surface moist. It should be noted that dead space impairs the wound healing process and predisposes the wound to abscess formation. Conversely, tight wound packing can impair circulation and damage healthy tissue.
In order to promote healing, it is necessary for the wound to be cleaned free of necrotic tissue. This tissue must be removed before healing takes place.
Non-adhesive polyurethane foam dressings such as ALLEVYN.RTM. and LYOFOAM.RTM. can be used on Stage II and Stage III wound types and provide some absorption while insulating the surface to prevent wound dehydration. It is specifically noted that these dressings should not be used with wound tunneling. Chronic Wound Care, .COPYRGT.1990, "Pressure Ulcer Management: A Nursing Challenge", Leslie A. Trudahl, p. 162.
Stage III and Stage IV ulcers heal by the process of granulation, wound contraction and epithelialization. Granulation involves the formation of collagen and new blood vessels. Regenerated collagen is not as elastic or strong as the dermis which has been destroyed. Wound contraction occurs when the wound edge pulls together at which time epithelization occurs.
Common factors that impair wound healing include the following:
Debridement of necrotic tissue in the wound is important because necrotic tissue harbors bacteria and prevents healing. Necrotic tissue includes slough, a yellow, green, or grey necrotic debris that looks like string and has a consistency of glue or chewing gum; and eschar, a thick, black, leather-like crust of dead tissue often covering an underlying necrotic process. Selective debridement is preferable to non-selective debridement in that selective debridement only removes necrotic tissue while non-selective debridement removes healthy, healing and necrotic tissues. Non-selective debridement includes wet-to-dry gauze dressings, dry-to-dry gauze packings, wet-to-wet gauze dressings, forceful irrigation, hydrogen peroxide, Dakin's solution, radical sharp debridement using scissors or knife, and whirlpool. Non-selective debridement is usually chosen for excessive necrotic debris and eschar and for debris supporting an infective process in the wound. Non-selective debridement sacrifices viable tissue for rapid cleaning of the wound.
Presently selective debridement includes careful surgical debridement and certain topical proteolytic enzyme preparations such as streptodornase, papain, sutilains, streptokinase, collagenase, fibrinolysin, and deoxyribonuclease, which digest and dissolve necrotic slough and eschars.
A number of patents have been directed towards treatment of necrotic tissue in wounds. Hyrogel wound dressings for preventing pooling of wound exudate are shown in U.S. Pat. Nos. 4,909,244; 5,115,801; and 5,160,328. Hydrogel dressings are composed of cross linked polymers (polyethylene oxide or polyvinyl-pyrrolidone ). Water usually constitutes more than 90% of the dressing's composition and the same are used on Stage I, II, or III pressure ulcers and dermal ulcers. A proteolytic enzyme dressing performs by separation of non-viable, devitalized tissue, especially eschar tissue from viable tissue in a host organ. Topical dressings for burn protection used in absorbing necrotic tissues and exudate are shown by U.S. Pat. No. 3,648,692. This patent has a wound facing layer of dressing constructed of any of various neutral synthetic reticulated open-cell solid foam or sponge materials and covered with a barrier membrane, the thickness of the sponge facing layer being critical (preferably about one-sixteenth of an inch ) so that debris, fluids, etc. contained therein are accessible for phagocytic invasion from the body surface. If the layer is too thick, U.S. Pat. No. 3,64 8,692 teaches that segregated exudate located at the interface is not reached by the natural phagocytic action with the undesirable result that infection takes place and spreads within the dressing thereby delaying or preventing the healing process. Another foam sponge product of lyophilized hydrocolloid foam capable of absorbing body exudates is shown in U.S. Pat. No. 4,292,972. A cross-linked collagen sponge for wound dressings which absorbs exudates is shown by U.S. Pat. No. 4,759,354. The wound dressing is preferably constructed of a thin outer oxygen and vapor-permeable film; a layer of an absorbent adhesive such as hydrogel for adhering the wound dressing to the skin and for acting as a reservoir for wound exudate absorbed therein; and a layer of collagen, in the form of a sponge or film adapted for placement directly on the wound, the collagen layer being of smaller dimensions than the absorbent adhesive layer so that areas of the adhesive layer extending beyond the periphery of the collagen layer can be applied to the skin surrounding the wound to adhere the dressing in place.
A debriding tape which contains a proteolytic enzyme preferably subtilisin A or B used in debridement of eschar and necrotic tissue is shown in U.S. Pat. No. 4,668,22 8. In this debriding tape, a thin polyether polyurethane film coated with an acrylate type surgical pressure sensitive adhesive has a release paper sheet covering the adhesive coating. An opening is cut in the release paper and subtilisin A powder is applied to the cut out area which is in turn covered with a protective facing of release paper. As taught by this patent a highly evaporative dressing cannot be used in the debriding tape as it is necessary for water from (or placed on) the wound being treated, to be held in place under the dressing so that it puddles and serves to activate the enzyme and is not transmitted through the dressing, wicking the enzyme away from the necrotic tissue. The debriding tapes are to be used to debride grade two to grade four ischemic ulcers, or any wound containing necrotic tissue.
A burn healing study published in 1962 by Chardack et al. was initiated with the knowledge that pores of an open cell sponge of formalinized polyvinyl alcohol when embedded in living tissues are rapidly permeated by granulation tissue. The clinical experiences of Chardack et al. supported the previous conclusions that an open cell (formalinized).sup.1 polyvinyl alcohol sponge becomes and remains adherent to a denuded body surface, whether the latter has resulted from the excision of integument in clean planes or whether it has been filled in by granulation tissue. The adherence of the sponge is predicated upon proliferation of viable granulation tissue into the pores of the sponge. Adherence was confirmed at the first time check point 24 hours after placement. The material can be repeatedly washed, cleansed and ultimately be replaced by autografts. Synthetic Substitutes For Skin, Chardack et al. Plastic & Reconstructive Surgery, Vol. 30, No. 5 (Nov. 1962). FNT .sup.1 added for edification
Autolysis is a method of selective debridement that has become accepted over the last several years as healthcare professionals have adopted theories of moist wound healing. Autolysis refers to self-digestion by the enzymes naturally present in wound fluids and the process of liquification of eschars. Autolysis could also be considered an organic technique because it enhances the body's own ability to rid itself of destroyed tissue. After debridement, wounds may become larger because all dead material has been removed which lays the ground work for healing to begin.
Four main types of synthetic dressings provide autolytic debriding action: